There's a lot of truth in the fact that thinking (and especially acting) positive can have a massive impact on you. But the problem is negativity comes natural and positivity... well... it requires WORK!
That leads us to believe it's not natural and it's not "us". Or maybe we get into the swing of it for a little while and then negativity creeps back in and we revert to our old ways?
Positivity is a skill! A skill that needs regular investment, just like any other. If we don't invest in it then negativity will naturally come and bite us in our collective arse!